Human visual function declines with age. A significant body of evidence suggests that much of this decline is associated with neuronal changes in the central visual pathways. The purpose of this proposal is, for the first time, to compare the functional organization of visual cortex and retina in young and old monkeys. The effects of aging upon the two main visual processing streams that comprise the primate retinogeniculocortical pathways will be studied. Two experiments are proposed in order to determine the neuronal bases of the age related decline in visual function that accompanies normal aging. These are outlined below. Experiment 1 will compare, in young and old monkeys, the receptive field properties of cells in cortical areas V1 (striate cortex) and V2. The properties to be studied include spatial resolution, contrast sensitivity, linearity of response, velocity sensitivity, binocularity, orientation sensitivity, direction sensitivity, wavelength sensitivity, receptive field size, receptive field organization (on and off sub- fields), response latency and response variability. The laminar locations of the cells studied will be determined as will their locations within functional compartments defined be cytochrome oxidase staining. Age related changes in receptive field properties will be related to the well documented declines in visual function associated with normal aging (see background ana significance). Experiment 2 will compare, in young and old monkeys, the properties of the two main morphological classes of retinal ganglion cells (M and P cells) projecting to the dorsal lateral geniculate nucleus. The cell body sizes, dendritic field structures, and retinal distributions of M and P cells will be studied quantitatively. The PI has been studying the morphology and receptive field properties of neurons in the mammalian visual pathways for twenty five years. The techniques required to carry out the proposed studies are constantly in use in his laboratory. In most cases, control data from normal animals has already been collected as a result of previous work. The proposed studies , thus, will undoubtedly yield valuable, clinically relevant data.